Method for efficiently enriching arsenic in wet-process phosphoric acid de-heavy residue acid

Abstract

The present application relates to the technical field of purification of wet-process phosphoric acid production, and discloses a method for efficiently enriching arsenic in heavy-slag-removing phosphoric acid, which comprises the following steps: S1, solid-liquid separation and hot water countercurrent washing to obtain heavy-slag-removed phosphoric acid; S2, adding the heavy-slag-removed phosphoric acid into a dilute hydrochloric acid decomposition solution, reacting, hot filtering to obtain a filtrate and a first-time filtered heavy-slag-removed phosphoric acid; S3, adding concentrated sulfuric acid into the filtrate, cooling and crystallizing, filtering, and returning the filtrate to S2 as the dilute hydrochloric acid decomposition solution; S4, repeating S2 with the first-time filtered heavy-slag-removed phosphoric acid, repeating S3 with the hot filtered filtrate, and hot filtering to obtain high-arsenic slag; and S5, adding the high-arsenic slag into concentrated sulfuric acid, boiling to collect overflow gas, washing the gas with concentrated sulfuric acid, and recovering arsenic in the sulfuric acid.

Description

Technical Field

[0001] This invention relates to the field of purification technology for wet-process phosphoric acid production, and in particular to a method for efficiently enriching arsenic in the heavy residue of wet-process phosphoric acid. Background Technology

[0002] The concentrated acid method for producing feed calcium phosphate involves reacting feed-grade phosphoric acid obtained by concentrating, removing weight and fluoride from wet-process phosphoric acid with calcium carbonate powder or emulsion, followed by drying, sieving and packaging.

[0003] Wet-process phosphoric acid is produced by decomposing phosphate rock with sulfuric acid, followed by filtration and concentration. Because phosphate rock contains a large amount of metallic impurities, during the concentration process, as the phosphoric acid concentration increases, the solubility of impurity ions decreases, the supersaturation increases, and crystals precipitate out, forming slag acid. Slag acid accounts for up to 16% of the actual phosphoric acid content. The slag acid precipitate is almost entirely composed of crystalline compounds, including Fe, Ca, Mg, Al, Na, K, F, Si, and SO42-. 2- These impurities play an important role in the formation of slag acid.

[0004] Because feed calcium phosphate products have requirements regarding the content of heavy metals such as arsenic and lead, which cannot exceed 30 ppm, wet-process phosphoric acid also needs to undergo a deweighting treatment. This is achieved by adding sodium sulfide solution to the phosphoric acid, causing arsenic and lead ions to react with sulfide ions to form heavy metal precipitates. These precipitates are then clarified and separated to remove the solid phase, including the heavy metal precipitates, from the acid, thereby reducing the heavy metal content in the acid. The main chemical reaction equations are as follows:

[0005] 2As 3+ +3S 2- →As2S3↓

[0006] Pb 2+ +S 2- →PbS↓

[0007] 2Na + +SiF6 2- →Na2SiF6↓

[0008] In addition to common compounds like CaSO4·2H2O and NaKSiF6, de-processed phosphate residue acid also contains heavy metal precipitates such as As2S3 and PbS. Previously, wet-processed phosphate residue acid was generally used to produce monoammonium phosphate or superphosphate fertilizers. However, the "GB 38400-2019 Limits for Toxic and Hazardous Substances in Fertilizers," issued on July 1, 2020, stipulates that the total arsenic content in inorganic fertilizers should be ≤50 mg / kg, and the total lead content ≤200 mg / kg. The arsenic content in de-processed phosphate residue acid is generally above 300 ppm, making it unsuitable for fertilizer production. Furthermore, conventional methods are insufficient to separate such low levels of arsenic, thus de-processing phosphate residue acid has become a significant challenge for the industry.

[0009] If arsenic can be efficiently separated from the acid in the desulfurized residue, not only can the phosphorus resources be utilized efficiently, but arsenic-containing compounds can also be recovered, which has significant economic and environmental benefits. Summary of the Invention

[0010] This invention provides a method for efficiently enriching arsenic in wet phosphoric acid deslag, solving the problem of difficult treatment and efficient utilization of existing deslag acid.

[0011] The solution of the present invention is:

[0012] A method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue includes the following steps:

[0013] S1. After solid-liquid separation, the obtained solid residue is washed with hot water countercurrently. After washing twice, the washing water is returned to the phosphoric acid system to obtain the de-heavy residue.

[0014] S2. Add the deweighted residue to the dilute hydrochloric acid decomposition solution, stir and react for 0.5 to 1 hour, and then hot filter to obtain the filtrate and the deweighted residue after one filtration.

[0015] S3. After adding an appropriate amount of concentrated sulfuric acid to the filtrate, cool and crystallize, filter, wash and dry the filter residue to obtain calcium sulfate dihydrate whisker product, and return the filtrate to S2 for use as a dilute hydrochloric acid decomposition solution.

[0016] S4. Repeat S2 with the heavy residue obtained from the first filtration, repeat S3 with the filtrate obtained from the hot filtration, and dry the filter residue obtained from the hot filtration to obtain high arsenic residue.

[0017] S5. Add the high-arsenic slag to concentrated sulfuric acid and boil for 5-10 minutes. Collect the gas that overflows during heating, wash the gas with concentrated sulfuric acid to obtain hydrogen fluoride gas and sulfuric acid enriched with arsenic, and recover the arsenic from the sulfuric acid. The arsenic in the sulfuric acid can be recovered by precipitation, microbial treatment, or other existing precipitation methods.

[0018] As a preferred technical solution, in step S1, a plate and frame filter press is used for solid-liquid separation; the hot water temperature for the hot water countercurrent washing is 60-100℃.

[0019] As a preferred technical solution, the dilute hydrochloric acid decomposition solution in S2 is a dilute hydrochloric acid with a medium mass concentration of 5-10%; the liquid-to-solid ratio of the dilute hydrochloric acid decomposition solution to the de-heavy residue is 8-12:1; and the stirring reaction temperature is 65-80℃.

[0020] As a preferred technical solution, the amount of concentrated sulfuric acid added in S3 is 2-5% of the total mass of the solution, and the solution includes concentrated sulfuric acid and filtrate.

[0021] As a preferred technical solution, the drying process is washing and drying.

[0022] As a preferred technical solution, the liquid-solid ratio of concentrated sulfuric acid to high-arsenic slag in S5 is 3 to 5:1.

[0023] This invention also discloses the application of a highly efficient method for enriching arsenic in the acid from wet phosphoric acid deslag. Arsenic is enriched and recovered by the method for enriching arsenic in the acid from wet phosphoric acid deslag, and calcium sulfate dihydrate whiskers and hydrogen fluoride gas are prepared.

[0024] Reaction mechanism:

[0025] Heavy metal-containing slag acid from the wet-process phosphoric acid production process can be effectively degraded by solid-liquid separation and hot water washing to remove phosphoric acid and soluble phosphates. The degraded slag is then decomposed with dilute hydrochloric acid to remove more than half of the gypsum dihydrate component, further enriching arsenic to obtain arsenic-containing solids. Simultaneously, the removed gypsum dihydrate is converted into calcium sulfate dihydrate whiskers. After drying, the arsenic-containing solids are heated to boiling with concentrated sulfuric acid for 5-10 minutes, causing fluorine to escape as hydrogen fluoride gas. Arsenic also escapes with the gas. The escaped gas is washed with concentrated sulfuric acid to obtain anhydrous hydrogen fluoride gas, while the arsenic remains in the washing sulfuric acid. The arsenic in the arsenic-containing sulfuric acid is then recovered using existing precipitation methods.

[0026] The beneficial effects of this invention are:

[0027] This invention provides a method for efficiently enriching arsenic in the acid from the wet phosphoric acid deslag process. By means of pressure filtration, washing, and acid decomposition, phosphoric acid, gypsum, and fluoride are gradually separated, and arsenic in the acid from the deslag process is enriched, thereby improving the recovery rate of phosphoric acid. Two high-value-added products, calcium sulfate dihydrate whiskers and anhydrous hydrogen fluoride, are produced as byproducts, improving the reuse rate of the acid from the deslag process. This method has good economic and environmental benefits. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0029] Example 1:

[0030] 1000 kg of wet-process phosphoric acid de-heavy residue with a P2O5 content of 30% and an As content of 180 ppm was filtered using a plate and frame filter press. The filter residue was washed twice countercurrently with 500 kg of hot water at 70-80℃ to obtain 140 kg of de-heavy residue with a solid content of 70%. The de-heavy residue was decomposed by stirring with 2800 kg of 10% hydrochloric acid at 75℃ for 1 hour. After filtration, 50 kg of concentrated sulfuric acid was added to the filtrate, and the mixture was allowed to cool naturally to crystallize. After filtration, washing, and drying, 40 kg of calcium sulfate dihydrate whiskers were obtained. The remaining high-arsenic residue was washed, dried, and 20 kg remained. 80 kg of concentrated sulfuric acid was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried with 5 kg of concentrated sulfuric acid. The collected anhydrous hydrogen fluoride gas product yielded concentrated sulfuric acid with an arsenic content of 3%.

[0031] Example 2:

[0032] 5000 kg of wet-process phosphoric acid de-heavy residue with a P2O5 content of 30% and an As content of 380 ppm was filtered using a plate and frame filter press. After two countercurrent washings with hot water, 880 kg of de-heavy residue with a solid content of 65% was obtained. The de-heavy residue was decomposed at 70°C for 1 hour using 16000 kg of 10% hydrochloric acid. The resulting decomposition liquid was added to 300 kg of concentrated sulfuric acid, allowed to cool naturally to crystallize, filtered, washed, and dried to obtain 190 kg of calcium sulfate dihydrate whiskers. The remaining high-arsenic residue was washed, dried, and 120 kg remained. 360 kg of concentrated sulfuric acid was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried using 20 kg of concentrated sulfuric acid. The resulting anhydrous hydrogen fluoride gas product was collected, along with concentrated sulfuric acid with an arsenic content of 8.6%.

[0033] Example 3:

[0034] 10 tons of wet-process phosphoric acid desiccant residue with a P2O5 content of 28% and an As content of 240 ppm was centrifuged using a high-speed centrifuge. After two countercurrent washings with hot water, 1360 kg of desiccant residue with a solid content of 72% was obtained. The desiccant residue was decomposed at 80°C for 0.8 hours using 2.8 tons of 10% hydrochloric acid. 500 kg of concentrated sulfuric acid was added to the decomposition liquid, and the mixture was allowed to cool naturally to crystallize. After filtration, washing, and drying, 420 kg of calcium sulfate dihydrate whiskers were obtained. The remaining high-arsenic residue was washed, dried, and 220 kg remained. 700 kg of concentrated sulfuric acid was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried using 50 kg of concentrated sulfuric acid. The resulting anhydrous hydrogen fluoride gas product was collected, along with concentrated sulfuric acid with an arsenic content of 4.2%.

[0035] Comparative Example 1

[0036] Same as Example 1, the only difference being that pressure filtration is not performed. Specifically:

[0037] 1000 kg of wet-process phosphoric acid de-heavy residue with a P2O5 content of 30% and an As content of 180 ppm was allowed to settle naturally. The supernatant was removed, and the lower solid layer was washed twice countercurrently with 500 kg of hot water at 70-80℃ to obtain 165 kg of de-heavy residue with a solid content of 60%. The de-heavy residue was decomposed by stirring with 2800 kg of 10% hydrochloric acid at 75℃ for 1 hour. After filtration, 50 kg of concentrated sulfuric acid was added to the filtrate, and the mixture was allowed to cool naturally to crystallize. After filtration, washing, and drying, 37 kg of calcium sulfate dihydrate whiskers were obtained. The remaining high-arsenic residue after filtration was washed, dried, and 23 kg remained. 80 kg of concentrated sulfuric acid was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried with 5 kg of concentrated sulfuric acid, and the resulting anhydrous hydrogen fluoride gas product was collected. Concentrated sulfuric acid with an arsenic content of 2.8% was also obtained.

[0038] Comparative Example 2

[0039] Same as Example 1, the only difference being that hot water backflow washing is not performed. Specifically:

[0040] 1000 kg of wet-process phosphoric acid de-heavy residue with a P2O5 content of 30% and an As content of 180 ppm was filtered using a plate and frame filter press to obtain 180 kg of de-heavy residue with a solid content of 55%. The de-heavy residue was decomposed by stirring with 2800 kg of 10% hydrochloric acid at 75°C for 1 hour. After filtration, 50 kg of concentrated sulfuric acid was added to the filtrate, and the mixture was allowed to cool naturally to crystallize. After filtration, washing, and drying, 36 kg of calcium sulfate dihydrate whiskers were obtained. The remaining high-arsenic residue after filtration was washed, dried, and 24 kg remained. 80 kg of concentrated sulfuric acid was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried with 5 kg of concentrated sulfuric acid, and the resulting anhydrous hydrogen fluoride gas product was collected. Concentrated sulfuric acid with an arsenic content of 2.7% was also obtained.

[0041] Comparative Example 3

[0042] Same as Example 1, the only difference being the use of 5% dilute hydrochloric acid, specifically:

[0043] 1000 kg of wet-process phosphoric acid de-heavy residue with a P2O5 content of 30% and an As content of 180 ppm was filtered using a plate and frame filter press. The filter residue was washed twice countercurrently with 500 kg of hot water at 70-80℃ to obtain 140 kg of de-heavy residue with a solid content of 70%. The de-heavy residue was decomposed by stirring with 2800 kg of 5% hydrochloric acid at 75℃ for 1 hour. After filtration, 50 kg of concentrated sulfuric acid was added to the filtrate, and the mixture was allowed to cool naturally to crystallize. After filtration, washing, and drying, 23 kg of calcium sulfate dihydrate whiskers were obtained. The remaining high-arsenic residue after filtration was washed, dried, and 35 kg remained. 80 kg of concentrated sulfuric acid was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried with 5 kg of concentrated sulfuric acid. The collected anhydrous hydrogen fluoride gas product yielded concentrated sulfuric acid with an arsenic content of 2.0%.

[0044] Comparative Example 5

[0045] Same as in Example 1, except that the liquid-to-solid ratio of concentrated sulfuric acid to high-arsenic slag in S5 is 2:1.

[0046] 1000 kg of wet-process phosphoric acid de-heavy residue with a P2O5 content of 30% and an As content of 180 ppm was filtered using a plate and frame filter press. The filter residue was washed twice countercurrently with 500 kg of hot water at 70-80℃ to obtain 140 kg of de-heavy residue with a solid content of 70%. The de-heavy residue was decomposed by stirring with 2800 kg of 10% hydrochloric acid at 75℃ for 1 hour. After filtration, 50 kg of concentrated sulfuric acid was added to the filtrate, and the mixture was allowed to cool naturally to crystallize. After filtration, washing, and drying, 40 kg of calcium sulfate dihydrate whiskers were obtained. The remaining high-arsenic residue was washed, dried, and 20 kg remained. 40 kg of concentrated sulfuric acid (the ratio of concentrated sulfuric acid to high-arsenic residue liquid to solids was added to the high-arsenic residue, and the mixture was heated to boiling for 10 minutes. The overflow gas was absorbed and dried with 5 kg of concentrated sulfuric acid, and the resulting anhydrous hydrogen fluoride gas product was collected. Concentrated sulfuric acid with an arsenic content of 2.4% was also obtained.

[0047] As can be seen from the above comparative examples, both pressure filtration and hot water countercurrent washing can improve the recovery of arsenic and facilitate the recovery of phosphorus. The appropriate concentration of dilute hydrochloric acid is more conducive to the recovery of calcium sulfate whiskers and also more conducive to the separation of arsenic in the sludge acid. The appropriate amount of concentrated sulfuric acid is also the key to the separation and recovery of arsenic.

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue, characterized in that, Includes the following steps: S1. After solid-liquid separation, the obtained solid residue is washed with hot water countercurrently. After washing twice, the washing water is returned to the phosphoric acid system to obtain the de-heavy residue. S2. Add the deweighted residue to the dilute hydrochloric acid decomposition solution, stir and react for 0.5 to 1 hour, and then hot filter to obtain the filtrate and the deweighted residue after one filtration. S3. After adding an appropriate amount of concentrated sulfuric acid to the filtrate, cool and crystallize, filter, wash and dry the filter residue to obtain calcium sulfate dihydrate whisker product, and return the filtrate to S2 for use as a dilute hydrochloric acid decomposition solution. S4. Repeat S2 with the heavy residue obtained from the first filtration, repeat S3 with the filtrate obtained from the hot filtration, and dry the filter residue obtained from the hot filtration to obtain high arsenic residue. S5. Add the high-arsenic slag to concentrated sulfuric acid and boil for 5-10 minutes. Collect the gas that overflows during heating, wash the gas with concentrated sulfuric acid to obtain hydrogen fluoride gas and arsenic-containing sulfuric acid, and recover the arsenic from the sulfuric acid.

2. The method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue as described in claim 1, characterized in that: In step S1, a plate and frame filter press is used for solid-liquid separation; the hot water temperature for the hot water countercurrent washing is 60-100℃.

3. The method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue as described in claim 1, characterized in that: The dilute hydrochloric acid decomposition solution in S2 is dilute hydrochloric acid with a mass concentration of 5-10%; the liquid-to-solid ratio of the dilute hydrochloric acid decomposition solution to the de-heavy residue is 8-12:1; and the stirring reaction temperature is 65-80℃.

4. The method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue as described in claim 1, characterized in that: The amount of concentrated sulfuric acid added in S3 is 2-5% of the total mass of the solution.

5. The method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue as described in claim 1, characterized in that: The drying process is washing and drying.

6. The method for efficiently enriching arsenic in wet-process phosphoric acid desulfurization residue as described in claim 1, characterized in that: The liquid-to-solid ratio of concentrated sulfuric acid to high-arsenic slag in S5 is 3-5:

1.

7. An application of a highly efficient method for enriching arsenic in wet-process phosphoric acid desulfurization residue, characterized in that: Arsenic is enriched and recovered by the method described in claim 1 for the efficient enrichment of arsenic in wet phosphoric acid desulfurization residue, and calcium sulfate dihydrate whiskers and hydrogen fluoride gas are prepared.